Multics and Related Honeywell 6000 Series Front Panels

Introduction

Multics
was a tremendously important operating system, from which (via Unix, which
was significantly influenced by it) most modern operating systems are
descended.

The first machine Multics ran on was the GE-645, using an extension to the
basic architecture of the GE 600 series CPUs; after GE's computer business
was sold to Honeywell, it then it ran on a number of models from the follow-on
Honeywell 6000 series.

Multics was born in the days when mainframes had lots of lights and switches,
and the early machines that it ran on were no exception; early Multics
hardware was festooned with lights.

A number of Web sites claim to have pictures of Multics panels, but... Alas,
the 6000 series included models that ran another OS, GCOS, and the CPUs (and
their front panels) are not the same; Multics CPUs included an extension called
the 'Appending Unit' to support both
virtual memory,
and Multics'
single-level store
architecture. A lot of pictures of 'Multics' front panels actually show
panels from GCOS machines.

To make things even more complicated, in the late 1970s Honeywell came up
with an alternative extension to the 6000 Series architecture, the so-called
'New System Architecture'. It added a new security architecture (using
domains, instead of the 'rings' of Multics), and also support for virtual
memory (which the basic 6000 series architecture did not have). A new version
of GCOS, GCOS 8, which came into use starting in 1980, made use of this.

So, this Web site attempts to show actual Multics panels; and also shows some
of the panels from GCOS and NSA machines which are confused with panels from
Multics machines.

Overall system architecture

A 6000 Series machine consisted of three classes of units: 'active' units,
'passive' units, and peripherals; only the first two will concern us here.
(Each instance of each of those was originally housed in a separate
free-standing cabinet.)

'Active' units included CPUs and IOMs (I/O controllers); the 'passive' units
are SCUs ('System Control Units', each of which contained a multi-port memory
controller, and the memory attached to that controller). A 6000 Series system
contained at least one CPU, one SCU and one IOM - and potentially many more
of any or all of them (7-CPU systems existed).

(Having multiple units of each type was good for system robustness - a system
could continue to operate, albeit with degraded peformance, if one unit of a
particular type had to be taken offline. It was also possible to split a
large system into two smaller working systems - a capability which was used
at several sites.)

Ports, Ports, Ports

There were no busses which connected multiple units together; all inter-unit
links were point-point, and required a separate 'port' in the units on each
end. In Multics, every active unit was required to be connected to all the
passive units.

So, in a system with 5 CPUs, 3 IOMs, and 6 SCUs, there would have been 30
separate CPUSCU links, and 18 IOMSCU links - and each CPU would have
had to have had 6 ports (one for each SCU), and each SCU would have required
8 ports (5 for the CPUs, and 3 for the IOMs).

This is important because early GCOS machines did not support the larger
configurations: e.g. CPUs and IOMs could hook up to at most 4 SCUs, so GCOS
CPUs had only 4 ports, and IOMs only 2. This means that early GCOS active
unit configuration panels only show a limited number of ports - making them
easy to tell apart from Multics panels.

The early Multics active units needed to be able to connect up to 8 SCUs,
because early SCUs contained a limited amount (256KW) of memory. Some of the
later NSA active units had more ports - e.g. the NSA IOM (below) had 8 ports.

When the later SCUs, which supported much more memory (4MW) arrived, machines
did not need as many SCUs. Since ports were expensive, the later active units
of both systems did not have as many ports - 4 ports, enough for 4 SCUs, was
plenty.

Panels, Panels, Panels

The front panels of the early units were huge; they were mounted on
the back of a large swing-out door, on the front of the unit's cabinet, and
they were very large - roughly 4' high, and 20" wide.

Most of the early front panels were divided into several 'sub-panels', for:

configuration

display

maintenance

test

functionality. In some cases, these took up too much room to be held on a
single maximum-sized physical front panel, and some sub-panels were housed in
a separate, apparently half-width, swing-out physical panel, here called a
'half-panel'.

It appears that there were basically three different generations of Honeywell
machines that ran Multics:

the 6180

the Series 60 Level 68 - a re-packaging of the 6180, in shorter cabinets

the DPS-8/M

The first two have the major front panels; in the third, all the
maintenance/etc sub-panel functionality had been moved to a console terminal,
driven by a micro-computer, the 'Diagnostics Processor Unit', which
interfaced to the various major units of the 6000 series (CPUs, SCUs and
IOMs); only the smaller configuration physical sub-panels were retained on
each type of unit.

(Most images below can be clicked on, to show a larger image.)

Multics CPU Panels

These panels are from Multics-specific CPU models, found only on Multics
machines.

In addition to the large maintenance panel (shown below), the early CPUs held
another, smaller, half-panel, the configuration panel, but we don't yet have
a good image of that entire half-panel (but see the image of the MIT 6180
system, below); we do have a (poor) image of the the Configuration sub-panel
of that half-panel, though (below).

We don't have an image of the maintenance panel from the later Series 60
Level 68 Multics CPU, but we do have (below) the corresponding Series 60
Level 66 GCOS CPU panel, which is identical to the 6000 series GCOS CPU
panel, except that it has changed from white to black, and the light bulbs
have been replaced with LEDs; the Multics CPU panel for the Level 68 probably
went through the same transformation.

Type

Comments

H6180 CPU Maintenance panel

Note the section at the top labeled 'Maintenance' - this is actually
the sub-panel for the 'Appending Unit', the special extension found only in
Multics CPUs.
This particular panel now belongs to the
Living Computers Museum,
where it has been hooked up to a Multics CPU simulator; a video of it
while Multics boots can be seen
here.

6000 Series / Level 68 Multics CPU Configuration panel

In GCOS CPUs, the CPU's Configuration sub-panel is part of the main
CPU physical front panel. In Multics CPUs, that space was taken up by
the sub-panel for the Appending Unit - and with more ports, the Multics
CPU's configuration panel was larger anyway, so it was apparently moved to
a separate half-panel.

DPS-8 Multics CPU Configuration panel

This seems to be functionally basically the same as the CPU Configuration
panel above, but with a panel 'look' consistent with the other DPS-8
panels.
Note, however, that it only supports 4 ports; by now, the larger SCU's were
ubiquitous, so there was no need for more than 4.

SCU Panels

These panels could be found on either Multics or GCOS machines; as far as is
known, the SCUs were identical for both.

Type

Comments

256KW SCU Configuration and Maintenance panel

4MW SCU Configuration and Maintenance panel

This is the later, larger capacity SCU; it apparently did not have
the full maintenance panel (as above), just this smaller
configuration/maintenance panel.

DPS-8 SCU Configuration panel

This is the SCU Configuration sub-panel for the DPS-8 machines;
it has a panel 'look' consistent with the other DPS-8 panels.

DPS-8 SCU Syndrome panel

This is an ancillary sub-panel to the DPS-8 SCU Configuration sub-panel
above, which displays memory error information.

IOM Panels

The Multics and GCOS IOM front panels were mostly similar, apparently with
only small differences in the Configuration sub-panel.

Type

Comments

GCOS IOM Configuration, Maintenance and Test panel

These panels were also probably mounted on the back of a large swing-out doors,
on the front of the IOM cabinet, and the same size as the early SCUs.
Note the limited number of ports.

NSA IOM Maintenance and Test panel

The NSA IOM Maintenance and Test panel appears to be indentical to the GCOS
one above, but it is missing the Configuration sub-panel of that, which has
been moved to a separate half-panel (below).
It is believed that the Multics IOM Maintenance and Test panel is
identical to this, but confirmation is currently unavailable.

NSA IOM Configuration and Bootload panel

The NSA IOM Configuration panel is identical to the original GCOS one,
but it has a lot more ports (i.e. can be used in a system with more SCUs,
i.e. more memory), so would no longer fit in the same panel, and had to be
moved.
It looks much the same as the Multics one below, but it is missing the two
sub-panels at the top of the Multics panel.

DPS-8 GCOS IOM Configuration and Bootload panel

This seems to be functionally basically the same as the NSA and Multics
IOM Configuration panels (above and below), but with a panel 'look'
consistent with the other DPS-8 panels.
Note that it only has 4 ports, standard for DPS-8 machines with both
Multics and GCOS.

Multics IOM Configuration and Bootload panel

Like the CPU Configuration, these panels (which supported 8 ports, i.e.
connection to 8 SCUs), and were thus pparently were too large to go where the
Configuration sub-panel went on a GCOS IOM front panel (above), so it was
moved to a separate half-panel, much like the CPU's.
One can be seen at the far right of the image of the MIT H6180 Multics
system, below.

DPS-8 Multics IOM Configuration and Bootload panel

This is the basically the same as the DPS-8 GCOS IOM Configuration
panel above. It is not clear with the minor differences between this one,
and the 'GCOS' IOM panel represent merely different temporal versions of
a universal DPS-8 IOM panel, or if the Multics and GCOS IOM panels were slightly
different.

Non-Multics CPU Panels

These panels are from CPU units which could be found only on GCOS machines.

Type

Comments

6000 Series GCOS CPU Configuration and Maintenance panel

This panel is the same size as the Multics CPU Maintenance panel, and
like those, was probably mounted on the back of a large swing-out door on
the front of the CPU cabinet,
Note that the large section at the top for the Multics Appending Unit is not
there; that space holds the Configuration sub-panel on these CPUs.

Level 66 CPU Configuration and Maintenance panel

Identical to the previous one, except for the colour, and lights.

Level 66 VU Configuration and Maintenance panel

The 'Virtual Unit' (VU) was the NSA counterpart to the Multics Appending
Unit (AU); apparently Series 60 CPUs could optionally have either an AU or
VU added to them. (The VU was standard on the later DPS-8 CPUs.) It too
apparently occupied its own half-panel.

Other Panels

These panels are from other units in the 6K line.

Type

Comments

6000 Series Microprogrammed Peripheral Controller panel

Originally, all disk drives, tape drives, etc were connected to IOMs via
mass storage and magnetic tape processors, respectively; those were eventually
replaced by this 'Microprogrammed Peripheral Controller'.

Multics Systems

Finally, some images of complete Multics systems - or, at least, as much
of them as will fit into a single image!

Type

Comments

H6180 Multics System at MIT

This image shows part of the dual-processor H6180 Multics system at MIT.
The unit on the far left is a 256KW SCU; to its right, there is a
6180 CPU.
Note the smaller panel just to the right of the CPU's maintenance panel
(mostly edge-on in this view); this is the 6180 CPU configuration half-panel
(which contains things moved from the top of the 60xx CPU maintenance panel
to make room for the Appending Unit sub-panel).
The panel visible in the distance at the right-hand edge of this
image is a Multics-type IOM's Configuration half-panel.

DPS-8/M Multics system at the University of Mainz

This shows the
Mainz Multics
system; that system included (from the left) an SCU, a CPU, another SCU, another CPU,
and an IOM.

See Also

Images of all the panels of the various generations of the Multics units
can be found in the "Multics System Maintenance Procedures Manual (AM81-04)",
a copy of which can been seen
here.